This invention relates in general to voltage generation circuits and in particular, to voltage generation circuits in flash EEPROM systems which are operative within a continuous voltage source range.
In certain applications, it may be desirable for a flash EEPROM system (or flash EEPROM plug-in card) to automatically accomodate either one of two voltage sources which may be connected to the EEPROM system. For example, in a normal mode of operation, a 5 volt voltage source compatible with logic circuitry in the EEPROM system may be connected to the EEPROM system, and in a battery mode of operation, a 3 volt voltage source may be connected to the EEPROM system and automatically accomodated by connecting after its detection, the 3 volt voltage source to a voltage doubler circuit in the EEPROM system.
The operational voltage range for such conventional flash EEPROM systems are typically specified as being discontinuous. For example, the range may be specified as 3 volts.+-.a tolerance (e.g., 5% or 10%), and 5 volts.+-.a tolerance (e.g., 5% or 10%). Intermediate voltages are generally not specified as being within the operational range of these conventional EEPROM systems. For example, with a 5% tolerance, voltages greater than 3.15 volts and less than 4.75 volts are not specified, and with a 10% tolerance, voltages greater than 3.3 volts and less than 4.5 volts are not specified.
In certain applications, however, it may be desirable for a flash EEPROM system (or flash EEPROM plug-in card) to automatically accomodate an arbitrary source voltage within a prespecified continuous range of source voltages. In these applications, the operational voltage source range is preferably specified as a continuous range from 3 to 5 volts.+-.tolerance (e.g., 5% or 10%).